1. Field of the Invention
The invention relates to illumination systems using filament lamps.
2. Description of the Related Art
On-axis reflector systems, such as e.g. elliptical and parabolic reflector systems, are often used in e.g. fiber optic illuminators, projection engines for large screen displays, and projection monitors. Such on-axis reflector systems may be used to couple electromagnetic radiation from a source into small targets. On-axis reflector systems, however, may magnify electromagnetic radiation emitted by the source in different amounts at different angles. The differences in magnification are exacerbated by the size of the light source. An ideal source for such an on-axis system is thus a point source.
Arc lamps are often used as sources of electromagnetic radiation in such systems rather than, e.g. filament lamps, because they are small enough to approximate a point source. Arc lamps are smaller than, e.g. filament lamps, because a, e.g. tungsten filament inside the filament lamp is generally longer than an arc of a comparable short arc lamp. If filament lamps were used in an on-axis reflector system, the image of the filament would be magnified differently for different angles of emitted radiation, resulting in a large fuzzy spot. Filament lamps are thus very inefficient for coupling light into small targets. Filament lamps, however, are generally less expensive, and last longer, than arc lamps. Filament lamps are thus generally used in on-axis reflector systems only if efficiency is not an issue. In applications where efficiency is not an issue a filament lamp such as, e.g. a large wattage lamp may be used.
There thus exists a need for a coupling system that can couple electro-magnetic radiation from a filament lamp at high efficiency into a small target.